The present invention relates to a single-layer type electrophotosensitive material, which is used in image forming apparatuses such as electrostatic copying machine, facsimile and laser beam printer. More particularly, the present invention relates to a single-layer type electrophotosensitive material, which is superior in wear resistance and has a long life.
In the image forming apparatuses described above, various photosensitive materials having the sensitivity within a wavelength range of a light source used in said apparatuses have been used. One of them is an inorganic photosensitive material using an inorganic material such as selenium in a photosensitive layer, while the other one is an organic photosensitive material (OPC) using an organic material in a photosensitive layer. Among these photosensitive materials, the organic photosensitive material has widely been studied because it is easily produced as compared with the inorganic photosensitive material and has a wide range of choice of photosensitive materials such as electric charge transferring material, electric charge generating material and binder resin as well as high functional design freedom.
The organic photosensitive materials are classified roughly into a so-called multi-layer type electrophotosensitive material (hereinafter abbreviated to a xe2x80x9cmulti-layer type photosensitive materialxe2x80x9d, sometimes) having a structure of an electric charge generating layer containing an electric charge generating material and an electric charge transferring layer containing an electric charge transferring material, which are mutually laminated, and a single-layer type photosensitive material (hereinafter abbreviated to a xe2x80x9csingle-layer type photosensitive materialxe2x80x9d, sometimes) wherein an electric charge generating material and an electric charge transferring material are dispersed in the same photosensitive layer. Among these organic photosensitive materials, it is a multi-layer type photosensitive material, which has a monopoly position in the wide market. The multi-layer type photosensitive material is exclusively a negative charging type photosensitive material comprising a conductive substrate, and an electric charge generating layer and an electric charge transferring layer formed in order on the conductive substrate.
On the other hand, the single-layer type photosensitive material has become of major interest recently because of its advantages described below. That is, the single-layer type photosensitive material is superior in productivity because of its simple layer construction and can inhibit the occurrence of layer defects of the photosensitive layer, and can also improve optical characteristics because of less interface between layers. Furthermore, one photosensitive material can be used as both of positive and negative charge type photosensitive materials by using, as the electric charge transferring material, an electron transferring material and a hole transferring material in combination.
The electrophotosensitive material is used in the repeated steps of charging, exposing, developing, transferring, cleaning and charge neutralizing in the image formation process. An electrostatic latent image formed by charging/exposure is developed with a toner as a powder in the form of microparticles. Furthermore, the developed toner is transferred to a transfer material such as paper in the transfer process. However, the toner is not transferred completely (100%) and is partially remained on the photosensitive material. If the remained toner is not removed, it is made impossible to obtain a high-quality image, which is free from contamination in the repeated processes. Therefore, it is required to clean the remained toner.
In the cleaning process, a fur brush, a magnetic brush or a blade is typically used. In view of the cleaning accuracy and rationalization of apparatus construction, it is general to select a blade cleaning wherein cleaning is performed by contacting a blade-shaped resin plate directly with a photosensitive material.
Although the blade cleaning has high accuracy, it increases a mechanical load on the photosensitive material, thereby causing problems such as increase in wear amount of the photosensitive layer, reduction in surface potential, lowering of the sensitivity and the like, thus making it difficult to obtain a high-quality image.
Unlike the multi-layer type photosensitive material, in case of the single-layer type electrophotosensitive material, the electric charge generating layer also exists on the outermost surface of the photosensitive layer as far as an overcoat layer is not formed. To the contrary, the electric charge generating layer is protected with the electric charge transferring layer in case of the negative charging multi-layer type photosensitive material. In case of the single-layer type photosensitive material, the electric charge generating material is often exposed to active gases such as ozone and NOx evolved in the image forming apparatus. Therefore, the charging capability of the photosensitive material is lowered and defects such as image fogging are likely to be caused by a reduction in surface potential.
In case of designing a so-called xe2x80x9clong-lifexe2x80x9d photosensitive material wherein image defects such as fogging do not occur even when printed a lot, there is disclosed a technique of using a resin having improved wear resistance, or various lubricants made of ester derivatives of stearic and lauric acids, fluororesin and the like. According to the technique described above, the wear resistance of the photosensitive layer is improved. However, it becomes difficult to scrape off the surface portion of the photosensitive layer, the charging capability of which is lowered by exposing to active gases such as ozone and NOx evolved in the image forming apparatus, thus making it impossible to obtain a xe2x80x9clong-lifexe2x80x9dphotosensitive material.
Japanese Published Unexamined Patent Application (Kokai Tokkyo Koho Hei) Nos. 5-333577, 5-333578, 5-333579 and 5-346674 disclose that a multi-layer type photosensitive material containing a specific electric charge generating material and polyethylene glycol having a molecular weight of 2000 or less in an electric charge generating layer is superior in charge stability. Since polyethylene glycol can also serve as a lubricant, it is expected that both of the wear resistance and the resistance to gases such as ozone and NOx are improved simultaneously when polyethylene glycol is applied to the single-layer type photosensitive material.
However, when polyethylene glycol is applied to the single-layer type photosensitive material, the sensitivity is drastically lowered. Therefore, it has been found that the resulting photosensitive material is not suited for practical use.
An object of the present invention is to provide a long-life single-layer type electrophotosensitive material, which is remarkably superior in wear resistance and sensitivity and is also superior in resistance to gases such as ozone and NOx.
In order to solve the problems described above, the present inventors have studied intensively and found a new fact that a long-life single-layer type electrophotosensitive material, which is remarkably superior in sensitivity and wear resistance and is also superior in resistance to gases such as ozone and NOx, can be obtained when incorporating a polyalkylene glycol compound whose terminal group is esterified or etherified, represented by the general formula [1]:
A1xe2x80x94Oxe2x80x94[(CH2)mxe2x80x94O]nxe2x80x94A2
wherein A1 and A2 are the same or different and represent an alkyl or aryl group having 1 to 50 carbon atoms, or a group: xe2x80x94COxe2x80x94R10 (R10 represents an alkyl or aryl group having 1 to 50 carbon atoms), m represents an integer of 1 to 5, and n represents an integer of 2 to 100, into a photosensitive layer. Thus, the present invention has been completed.
That is, the single-layer type electrophotosensitive material of the present invention comprises a conductive substrate, and a photosensitive layer made of a binder resin containing at least an electric charge generating material and an electric charge transferring material formed on said conductive substrate, said photosensitive layer containing a polyalkylene glycol compound whose terminal group is esterified or etherified, represented by the general formula [1].
According to the present invention, a pseudo-three-dimensional network is formed by a bonding a hydrophilic functional group (e.g. hydroxyl group, carbonyl group, etc.) in the binder resin with an ester or ether group in a polyalkylene glycol compound represented by the general formula [1] by means of a van der Waal""s force, a hydrogen bond or a chemical bond, in addition to a mere role of the polyalkylene compound as a lubricant, and the film hardness of the binder resin, in its turn the entire photosensitive layer, thus making it possible to obtain a single-layer type electrophotosensitive material which is less likely to cause wear, that is, an electrophotosensitive material having excellent wear resistance.
Since the formation of the above net work reduces micropores on the surface of the photosensitive layer, gases such as ozone and NOx are less likely to penetrate into the photosensitive layer from the surface of the photosensitive layer, thereby improving the gas resistance.